In conventional outboard steering systems for marine vessels, the propulsion units are mounted low enough on the marine vessel so as not to cause cavitation while operating in choppy waters or while executing turns. The propulsion units may be mounted higher when the marine vessel is operating on a straight course in calm waters. However, outboard propulsion units are conventionally bolted to the transom of the marine vessel which prevents movement of the propulsion units readily up or down. The propulsion units may also be trimmed upwardly to run in shallow water to avoid contacting the bottom or weeds. However, trimming a propulsion unit upwardly may place the cavitation plate in front of the propeller, thereby encouraging cavitation. Furthermore, an upwardly trimmed propulsion unit may cause a spray of water to shoot up into the air, which is indicative of a waste of energy. Additionally, an upwardly trimmed propulsion unit may cause a downward thrust on the marine vessel which pushes the marine vessel down, particularly at the stern. This may raise the bow and lower the stern of the marine vessel, making the draft of the marine vessel deeper.
In contrast, raising a propulsion unit vertically keeps the cavitation plate above the propeller and aligned with the movement of the marine vessel. Jack plates have accordingly been developed to allow outboard propulsion units to be raised vertically while running in shallow water to avoid the negative consequences of trimming propulsion units. Typically the propulsion units are positioned so as to be just on the verge of cavitation which allows the marine vessel to run and start up in far shallower depths. However, one of the concerns commonly encountered with the use of jack plates is for an operator to know the precise height of the propulsion unit. Typically the jack plate is adjusted manually and the operator may use a gauge as a visual indicator of the height of the propulsion unit. There is however a risk of positioning the propulsion unit too high to make a safe turn. The propulsion unit may also be raised so the cooling water intake is raised above the surface of the water, risking overheating of the propulsion unit. Most operators typically therefore compromise toward safety and use a manual jack plate at a safer, lower level which forfeits some of the potential speed gains.
Another issue with the use of jack plates is that the propulsion unit is positioned more outwardly relative to the marine vessel since the propulsion unit is connected to the transom via the jack plate. This may cause the propulsion unit to no longer clear the top of the transom when fully tilted out of the water. Consequently, when the jack plate is fully lowered, the propulsion unit or the steering cylinder may collide with the transom or the jack plate, possibly causing damage to the propulsion unit or the steering cylinder. This is a major safety concern.
There is accordingly a need for an improved jack plate and controls therefor which permit the jack plate to be adjusted readily while the marine vessel is in operation and, at the same time, provide an operator with reliable feedback as to the position of the jack plate without requiring the height of the propulsion unit to be measured or requiring the operator to visually refer to a gauge, which may be difficult while operating the marine vessel.